can: let SJA1000 driver depend on HAS_IOMEM

Fixes this compile error on s390:

drivers/net/can/sja1000/sja1000_platform.c: In function 'sp_read_reg':
drivers/net/can/sja1000/sja1000_platform.c:42: error: implicit declaration of function 'ioread8'
drivers/net/can/sja1000/sja1000_platform.c: In function 'sp_write_reg':
drivers/net/can/sja1000/sja1000_platform.c:47: error: implicit declaration of function 'iowrite8'
drivers/net/can/sja1000/sja1000_platform.c: In function 'sp_probe':
drivers/net/can/sja1000/sja1000_platform.c:79: error: implicit declaration of function 'ioremap_nocache'

Cc: Wolfgang Grandegger <wg@grandegger.com>
Cc: Oliver Hartkopp <oliver.hartkopp@volkswagen.de>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>